No special bonus is gained by the wearing of multiple pieces of this set.
To be able to buy this armor set from Keortor Talyse (outside the entrance to The Infernal Forge of Ages in Solusek's Eye at ( -69, -626, -59 ) /waypoint -68.56, -626.30, -58.67) you will need to obtain an armor component (dropped in the Kingdom of Sky raid instances) and three gem components (dropped in the Kingdom of Sky heroic instances) per item, i.e.: